Geologists view the part of our planet that is called the ______________ as consisting of a number of close-fitting plates
a. mesosphere
b. lithosphere
c. asthenosphere
d. none of these
b
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Light rays from a distant source __________________, assuming the light does not pass through any cloud-like nebulae
a. are perpendicular b. focus to an image c. focus to a point d. are parallel
A light oil flows through a copper tube of 2.6-cm-ID and 3.2-cm-OD. Air flows perpendicular over the exterior of the tube as shown in the following sketch. The convection heat transfer coefficient for the oil is 120 W/(m2 K) and for the air is 35 W/(m2 K). Calculate the overall heat transfer coefficient based on the outside area of the tube (a) considering the thermal resistance of the tube, (b) neglecting the resistance of the tube.
GIVEN
• Air flow over a copper tube with oil flow within the tube
• Tube diameters
? Inside (Di) = 2.6 cm = 0.026 m
? Outside (Do) = 3.2 cm = 0.032 m
• Convective heat transfer coefficients
? Oil h i= 120 W/(m2 K)
? Air h o= 35 W/(m2 K)
FIND
• The overall heat transfer coefficient based on the outside tube area (Uo), (a) considering the thermal resistance of the tube, and (b) neglecting the tube resistance
ASSUMPTIONS
• Uniform heat transfer coefficients
• Variation of thermal properties is negligible
SKETCH
PROPERTIES AND CONSTANTS
the thermal conductivity of copper (k) = 392 W/(m K) (at 127°C)
A sinusoidally varying potential difference has amplitude 170 V. What is its minimum instantaneous value?
1.170 V 2.120 V 3.0 4.-120 V 5.-170 V
What type of particle accelerator has two large D-shaped electrodes with a small gap between them, through which an alternating potential difference accelerates the particles in a constant magnetic field?
A) linear accelerator B) synchrotron C) cyclotron D) None of the above